This application relates to manually operated control devices, and more particularly to a knob-like control device adapted for installation on existing control units to convert a lever type control action to a twisting or turning action.
On heavy trucks or tractors for freight trailers and the like the engine transmission is controlled, at least in part, by a pneumatic shift control. Such controls in general comprise a pedestal at the driver's station with a head supporting a pneumatic valve with a movable lever control. Air lines from the latter valve extend from control head to actuators at the transmission. In normal operation, a driver used his fingers and/or thumb to move the control lever to different shift positions, and often this caused physical impairment or discomfort of the driver's hand particularly when driving in traffic.
Another problem which arose with this conventional shift lever was the tendency of a driver to move the relatively small shift lever into a low gear position accidentally when the vehicle was moving at a relatively high rate of speed. Once the control lever is moved so that pneumatic power is released, a grinding of gears causing excessive wear and possibly total failure or heavy damage to the transmission could easily occur. With many such pneumatic transmission control systems in service this seemingly simple control lever became a significant problem. Yet it would have been expensive and time consuming to alter the entire shift system.